The present invention relates to the field of sensor systems, and in particular to a technique for programming a sensor, such as a magnetic field sensor, for example a linear Hall effect sensor.
Conventional sensor systems are described, for example, in “Hütte—die Grundlagen der Ingenieurwissenschaften, Herausgeber: Akademischer Verein Hütte e. v., Berlin, edited by Horst Czichos, 30th newly revised and expanded edition, Berlin: Springer Verlag 1996, page H 18 ff” [Hütte—Basic Principles of the Engineering Sciences]. This publication discloses a sensor system that contains a sensor unit and an analytical unit. The sensor unit includes at least one sensor element that senses a measurement variable and generates a sensor signal representing this measurement variable. A sensor-signal processing unit then receives and processes the sensor signal. The function of the analytical unit is to analyze the sensor signals processed by the sensor processing unit.
There are a plurality of prior-art sensor types. These include, for example, four main types such as:
(i) sensors whose signals are processed in the sensor-signal processing unit in accordance with fixed algorithms (type 1); (ii) sensors whose signal processing in the sensor-signal processing unit can be freely programmed (type P); (iii) sensors whose signal processing is regulated (type R); and (iv) sensors whose signal processing in the sensor-signal processing unit can be both programmed and regulated. We shall now briefly describe these prior art sensor types:
Sensors with Fixed Signal Processing Algorithms
The most widespread sensor systems convert a generally analog physical or chemical measurement variable (M) into an output signal in accordance with fixed prescribed algorithms. Physical measurement variables can be, for example, pressure, temperature, and magnetic field. Chemical measurement variables can be, for example, the chemical reaction rate and the reaction enthalpy, or the like.
The sensor element typically converts the physical (or chemical) measurement variable (M) into an internal voltage signal U(M). However, it is also possible to generate a current signal or an optical signal that is indicative of the measurement variable M.
The sensors discussed hereinafter shall be discussed in the context of sensors that convert a physical measurement variable M into an internal voltage signal U(M). The amplitude of the internal voltage signal U(M) represents the physical measurement variable M. However, this assumption is made without any restriction of generality.
The output signal (Out) of most sensor units is proportional to the measurement variable M. However, especially in the case of magnetic field sensors, there are types which transform an analog measurement variable M into an output signal (Out) which has only two states. These are generally called switching sensors. Such switching sensor units have two fixed prescribed threshold values G1 and G2. In the following, we assume G1>G2. In the output, these generate a signal Out=“1” if the internal voltage signal U(M)>G1, and an output signal Out=“0” if U(M)<G2:
                              Out          new                =                  {                                                                      1                  ,                                      if                    ⁢                                                                                  ⁢                                          (                                                                                                    U                            ⁡                                                          (                              M                              )                                                                                >                                                                                    G                              1                                                        ⁢                            Δ                            ⁢                                                                                                                  ⁢                                                          Out                              old                                                                                                      =                        0                                            )                                                                                                                                            0                  ,                                      if                    ⁢                                                                                  ⁢                                          (                                                                                                    U                            ⁡                                                          (                              M                              )                                                                                <                                                                                    G                              2                                                        ⁢                            Δ                            ⁢                                                                                                                  ⁢                                                          Out                              old                                                                                                      =                        1                                            )                                                                                                                              (        1        )            Sensor System with Freely Programmable Algoritms
Besides sensor units in which the sensor signal is processed in accordance with fixed algorithms, there are types in which the processing algorithm can be freely programmed by fixed prescribed parameters. These fixed prescribed parameters are stored for example, in EEPROM cells, which are situated on the same chip as the other components of the sensor unit (e.g., the sensor element and the sensor-signal processing unit). An example of this is the analog sensor of the construction series HAL800 manufactured by Micronas GmbH, the assignee of the present invention. Its analog output signal can be programmed in the parameters C1 and C2 asOut=c1*U(M)+c2  (2)Its advantage compared to the sensor systems with fixed signal processing algorithms is that the programming can reduce production-based variations and influences due to the interactions of the sensor system with its action.
Once the programming process is concluded, the sensor unit behaves like a sensor unit with a fixed signal processing algorithm as discussed above. Accordingly, the sensor unit has fixed settings by which the measurement variable M is converted into an output signal Out. However, a problem with this technique is that the programming adjustments can no longer be changed, that is, this state is technically called “locked.”
Sensor Units with Control Algorithms
In a third class of sensor units, the sensor-signal processing unit operates with internal regulation algorithms. Such regulation algorithms convert a time-variable, analog, internal voltage signal U(M,t) into an output signal Out. The time dependence of the internal voltage signal U(M) is identified by the reference symbol t.
For example, there exist adaptive magnetic field sensors in which the internal voltage signal U(M) is subjected to high-pass filtering. Specifically, the DC component of the internal voltage signal U(M) is attenuated, and in the ideal case only a sinusoidal alternating signal U(MAC) remains. If this remaining sinusoidal alternating signal exceeds a given threshold G1, then—as in the example described above—an output state Out=“ 1” is generated. However, if the AC component is less than a second threshold G2, the output signal Out=“0” is generated. The mathematical representation of such a generation of the output signal is given by equation (3) as follows:
                                          U            ⁡                          (                              M                AC                            )                                ⇒                                    U              ⁡                              (                M                )                                      -                                          ∫                                  t                  1                                                  t                  2                                            ⁢                                                U                  ⁡                                      (                    M                    )                                                  ⁢                                                                  ⁢                                  ⅆ                  t                                                                    ⁢                                  ⁢                              Out            new                    =                      {                                                                                1                    ,                                          if                      ⁢                                                                                          ⁢                                              (                                                                                                            U                              ⁡                                                              (                                                                  M                                  AC                                                                )                                                                                      >                                                                                          G                                1                                                            ⁢                              Δ                              ⁢                                                                                                                          ⁢                                                              Out                                old                                                                                                              =                          0                                                )                                                                                                                                                              0                    ,                                          if                      ⁢                                                                                          ⁢                                              (                                                                                                            U                              ⁡                                                              (                                                                  M                                  AC                                                                )                                                                                      <                                                                                          G                                2                                                            ⁢                              Δ                              ⁢                                                                                                                          ⁢                                                              Out                                old                                                                                                              =                          1                                                )                                                                                                                                                    (        3        )            Sensors of this type, in contrast to the previous two types discussed above, also take into account the time behavior of the measurement variable M.Sensors with Programmable Regulation Algorithms
This fourth class of sensor units is a combination of the type with freely programmable algorithms and the type with control algorithms. Sensors of type with programmable regulation algorithms consequently combine the advantages of a sensor unit of the type with freely programmable algorithms and of a sensor unit of the type with control algorithms. Since signal processing is freely programmable, one can compensate the tolerances of a total system, consisting of mechanical components and the actual sensor system. However, as the result of regulation, the output signal Out will react to the instantaneous time behavior of the measurement variable M(t). Conventional sensor systems preferably operate by the latter method. However, a problem with this technique is that changes of the sensor system are no longer compensated, especially of the sensor element, within the lifetime of the sensor unit.
Therefore, there is a need for a sensor that can be programmed to compensate for changes in the sensor system that occur throughout the operating life of the sensor.